[foo][ref[bar]]

[ref[bar]]: /uri


----------

(Document
  (Paragraph
    '['
    'foo'
    ']'
    '['
    'ref'
    '['
    'bar'
    ']'
    ']')
  (Paragraph
    '['
    'ref'
    '['
    'bar'
    ']'
    ']'
    ': /uri'))
